Fix Win builds

Author: sobolevn

PCbuild/_testcapi.vcxproj

@@ -102,6 +102,7 @@
     <ClCompile Include="..\Modules\_testcapi\abstract.c" />
     <ClCompile Include="..\Modules\_testcapi\unicode.c" />
     <ClCompile Include="..\Modules\_testcapi\dict.c" />
+    <ClCompile Include="..\Modules\_testcapi\set.c" />
     <ClCompile Include="..\Modules\_testcapi\datetime.c" />
     <ClCompile Include="..\Modules\_testcapi\docstring.c" />
     <ClCompile Include="..\Modules\_testcapi\mem.c" />